1. Field of the Invention
The present invention relates to technology of forming a coating film on a surface of a substrate, and more particularly to technology of drying a coating film formed on a surface to be coated of a substrate held in a state where the surface to be coated faces down in a clean room in which down flow is constituted.
2. Description of the Related Art
Conventionally, as a coating apparatus (coater) which coats on a coating liquid such as photoresist or the like a substrate such as a silicon wafer or the like, a coater in which a coating liquid is dropped in the center of a substrate, and then the substrate is rotated at a high speed thereby to spread the coating liquid on a surface of the substrate by centrifugal force and form a coating film on the substrate surface, which is called spin coater, is mainly used.
On the other hand, recently, technology of forming a coating film with more exact thickness is desired according to more minute patterns and larger size of a photomask used in manufacture of a liquid crystal display. In this view, as a coating apparatus, for example, a CAP coater as disclosed in Japanese Patent Laid-Open No. 2001-62370 is also provided.
In this CAP coater, a nozzle having a capillary gap is sunk in a liquid tank storing a coating liquid therein, the nozzle is raised up to the vicinity of a surface to be coated of a substrate held by an absorption board in a state that the surface to be coated looks downward, the coating liquid is applied from the capillary action gap, and then the nozzle scans over the surface to be coated, whereby a coating film is formed. Herein, since the coating thickness can be surely adjusted by the distance between the surface to be coated and the leading end of the nozzle, the film thickness can be set more exactly than in the spin coater.
Further, since this CAP coater includes a turn mechanism that rotates the absorption board up and down, when the substrate is set, the absorption board is turned until the absorption surface looks up, and the substrate is placed so that the surface to be coated looks up on the absorption surface. Therefore, the CAP coater has such convenience that after the substrate has been thus set, the absorption board is turned until the absorption surface looks down again thereby to perform coating.
On the other hand, though this CAP coater has the above convenience, the absorption board frequently moves slightly even during coating due to backlash in the turn mechanism, which negatively influences the quality of the thin film.
In order to avoid this problem, by fixing the absorption board in a state where the absorption surface looks down, the absorption board is always kept horizontal. Therefore, unsteadiness of the substrate can be surely prevented, so that yield can be improved. Therefore, realization of such the technology is desired.
However, the realization of this technology has the following problems.
Namely, in a clean room in which down flow is constituted, as schematically shown in FIG. 16, air flow D of the down flow is shut out on the upper surface of an absorption board 71, the shut-out air flow D turns to an absorption surface 71a side, and air eddy is formed there. In case that the absorption board 71 is fixed in the state where the absorption surface 71a looks down, since a surface to be coated 72a of a substrate 72 always looks down, the coating film is subjected to the air eddy. Accordingly, after coating, when the coating film is dried by down flow, unevenness of the film thickness is produced by the air eddy.